Can you find the star that is shining close to the big and bright waxing gibbous moon[3] tonight? That is Regulus, the brightest star in the constellation Leo the Lion. Regulus[4] is the only first-magnitude star to sit almost exactly on the ecliptic.

The ecliptic is the Earth’s orbital plane projected outward onto the sphere of stars. The ecliptic is often shown on sky charts, because the moon and planets are always found on or near the ecliptic.

Four first-magnitude stars reside close enough to the ecliptic to be occulted – covered over – by the moon on occasion: Regulus, Spica[5], Antares[6] and Aldebaran[7]. In fact, the moon occulted Antares during January and February of 2010. Although no more lunar occultations of first-magnitude stars are in the works for this year, lunar occultations of bright stars are not uncommon. However, an occultation of a first-magnitude star by a planet is extremely rare. The last time a planet occulted a first-magnitude star was when Venus occulted Regulus on July 7, 1959. The next time will be when Venus occults Regulus on October 1, 2044.

Before 1959, the most recent planet/first-magnitude star occultation took place on November 10, 1783, when Venus occulted Spica. Venus will again occult Spica on September 2, 2197.